LVDT linear sensors.

A new product addition to the Hoffmann + Krippner redesigned, user-friendly online shop has been announced. In addition to Sensofoil linear and rotary membrane potentiometers, cleanroom / medical keyboards and emPC A/RPI Industrial PCs, the shop now features inelta LVDT linear displacement sensors.

The new online inelta portfolio ranges from standard and miniature displacement sensors to sensors with integrated signal processing and external thread for easy installation.

The IZAL Series miniature sensors, for example, are ideal for medical, industrial, testing, agricultural and military applications. The contactless, wear-free sensors for displacement and position detection achieve a linearity tolerance of ± 0.5% (optionally 0.25%) and are designed for the extremely small measuring ranges of 2, 5 and 10mm.

The new H+K online shop is easy to navigate and provides unique product specifications as they pertain to each of the LVDT categories, allowing the customers to quickly find the perfect linear displacement sensor for their application.

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Tiny iInductive path sensors.

The new Inelta ILAT Series Miniature LVDT Sensors provide precision measurements of position and path in the range of single-digit millimeters. The sensors of this series are available in Models ILAT 2, ILAT4 and ILAT10 for the exact measurements of ±1 mm, ±2 mm or ±5 mm traveling distances.

Owing to their tiny dimensions with a housing length of 79 mm and a diameter of only 8 mm at a weight of 30 g (including cable), the sensors will navigate even within very tight-fitting conditions.

Because of the inductive LVDT principle (Linear Variable Differential Transformer), in which a coil within the sensor with a primary winding and two secondary windings transforms the linear motions of the measuring sensor contact-free into a single electronic signal, the ILAT Sensors operate free from wear and provide a linearity tolerance of >0.25 They are also available with an even smaller linearity tolerance of >0.1%.

Even with their tiny dimensions, the ILAT Sensors are distinguished by their robust design with a stainless-steel housing in protection class IP65 – optionally also in IP67. Nominal temperature rating is 0° – 70°C. The carefully designed linear guiding operates by virtue of a locking mechanism of the probe and can provide more than 10 million cycles. These versatile sensors are suitable for many applications, including medical technology, engineering, agriculture and navigation up to testing facilities or manufacture of special purpose machinery.

Fitting the ILAT Path Sensors are the Inelta external sensor amplifiers IMA2-LVDT, available for signals in the ranges of 0..5V, 0..10V, ±5V, ±10V, 0/4..20mA and ISM-LVDT for 0…10V- or 0..20mA signals. Our print module IVM-LVDT with a readout of 0..10V signals, is also available, suitable for integration into your electronics.

Additionally, Inelta can provide custom sensor designs with further optional features such as custom-made calibration, cable lengths and expanded temperature ranges.

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Position sensors for medical, testing and industrial applications.

Hoffmann – Krippner offers a wide range of LVDT sensors from its German partner company INELTA for contactless and wear-free path and position detection.

The LVDT sensors operate on the principle of the differential transformer and are suitable for use in many applications, such as medical technology, industrial, seafaring, in testing facilities, machinery construction, special purpose machines and agriculture.

Thanks to the housing made from chemically nickel-plated steel with IP65 type of protection (optional IP68) and a temperature range of -25 to +85°C, which can be expanded on request, the LVDT sensors are suitable for use in harsh environments. Due to their external thread, the devices are easily installed and adjusted. Unlike competing smooth designs, there is no need for them to be clamped with grub screws which can damage the housing and distort the measured value. The connection takes place via a M12 connector or a cable.

They are available as M12 or M18 versions with external thread and capture measuring lengths of up to 2, 5, 10 or 20 mm, depending on the model. It is actuated by an unguided core or a switch with internal spring. The linearity tolerance of the sensors is ± 0.5%.

The M18 sensors come with integrated electronics and a current or voltage output. For the M12 models, users can choose between various signal amplifiers which generate output signals ranging from 0 to 5 V, 0 to 10 V, ± 5 V, ± 10 V, 0 to 20mA or 4 to 20mA.

Custom sensor designs with other configuration options, such as improved linearity tolerance or individual calibrations, are also available.  An online configuration guide and questionnaire with optional capabilities are provided to make it easy for design engineers to create their own custom designs.

Tired bridges?

Research into bridge fatigue behaviour relies on RDP transducers

An important research programme to help predict the future life expectancy of masonry bridges is being conducted at the University of the West of England using load cells and LVDTs supplied by RDP Electronics.

In Britain and throughout Europe a very large proportion of the bridge stock is of masonary arch construction, built in the heyday of canal and railways era well over a century ago, when traffic movements and vehicle loading were significantly lighter than today. Predicting the projected life span and fatigue limits of these old bridges are becoming of increasing interest for bridge owners and providing material test data on the long-term behaviour of brick masonry a necessary requirement.

A research programme at the University of the West of England led by Dr Adrienn Tomor and was funded by the Engineering and Physical Sciences Research Council (EPSRC) studies the failure of representative examples of bricks for masonry arch bridges. Typical masonry types have been classified into three categories. The weakest category was widely used for the canals, were typically hand-made using locally sourced clay and varied widely in strength, even within the same bridge. By the time railways were constructed, industrial processes compacted the clay, leading to more consistent bricks, classified in the project as ‘medium’ strength. Finally, “strong” bricks are representative of today’s industrially manufactured bricks.

The main load bearing element of masonry arch bridges is the arch ring, in which the stresses can change significantly with the passing traffic. For areas with high stress concentration, long-term loading can lead to gradual deterioration of the material over time. Representative small-scale brick samples have been tested up to failure under compression and sheer within the test series, to help establish a relationship between stress levels and life excpectancy. Various RDP Electronics transducers are used in the test rigs, including RLU 5,000 kg load cells, GT 1000-L10 and GT2500RA-L10 LVDTs selected based on suitable precision, ease of installation and cost.

LVDTs well suited to capture high speed and high frequency movement

Due to their fundamental design and mode of operation LVDT's are very suitable for measuring high speed and high frequency movements on mechanical structures.

Applications calling for high frequency movements include switch testing, recoil testing, blast testing and high frequency component testing. It is important not to confuse sample rate with frequency response. The parameter being measured is the analogue frequency response, so that, for example, a mechanical oscillation of 500 repetitions per second would be faithfully reproduced by the LVDT output. A typical RDP LVDT and amplifier combination can have a mechanical frequency response of up to 500 Hz. Where applications need to go faster, this can be enabled by modifications to the signal conditioning electronics.

LVDTs are available in ‘spring return’, ‘guided’ and ‘unguided’ mechanical configurations which determine the LVDT frequency response. A spring return type is limited by the ratio of the mass of the amplifier compared to the strength of the spring which typically on a short transducer imposes a limit of the order of 10 Hz. A captive type transducer is not restricted in this way but since it contains guidance bearings if exposed to multi-millions of cycles, will eventually show signs of wear. Consequently the preferred transducer configuration to use for high frequency applications is the unguided type. This version can be arranged to make physical contact between the armature and the body of the transducer and so can operate indefinitely at high frequencies.

LVDT arrays help measure structural floor deflection

RDP Electronics are often called on to supply arrays of LVDTs for situations where it is important to measure the structural strength of floors.

A common requirement is for the strength of the floor to be determined when a indication of loading is required. Alternatively, for otherwise routine testing of structural floors inside buildings, or for concrete beams and structures inside railway stations for example, where it is necessary to measure how much the floor structure moves when a load is applied. The systems supplied by RDP involve an array of LVDT's and usually measure the frame above the floor before the floor is loaded, and the deflection is then monitored at various points. RDP has a comprehensive range of LVDTS which employ an operating principle that requires no electrical contact across the transducer position sensing element which for the user of the sensor means clean data, infinite resolution and a very long life. RDP has several decades of experience in the research, development and manufacture of LVDTs to internationally recognised quality standards.

Transducers for sea floor valve control are built for high reliability

Transducers embodied in valves used for controlling oil flow in undersea pipelines have been developed by RDP Electronics to operate with high accuracy and high reliability.

RDP’s LVDTs are supplied to several valve manufacturers for use with valves controlling the flow of oil from pipe networks on the bottom of the sea, close to the well head. The transducers are usually sealed within the valve and are required to withstand very high pressures of up to 5000 psi. One construction option is to ventilate the transducer, allowing the oil to flow freely through the transducer, providing fluids are non-conductive and non-corrosive.

Ventilated LVDT transducers are used in conjunction with sealed amplifiers and are also immersed in the oil. Alternatively sealed transducers can be provided that are manufactured with a fully welded construction. In all cases the transducers are subjected to a very high level of production testing, including pressure testing in both water and in helium, shock and vibration testing and repeated temperature cycles at many points in the production process to ensure minimal failure rates in the field. RDP’s onerous testing regime has achieved extremely high reliability rates for these LVDTs, with less than 1 failure in 2000 units per year.

Impact safety!

Magnetostrictive displacement transducers prove popular for impact testing
          
Impact testing of safety products such as crash helmets, calls for accurate measurement of displacement which is achieved by using transducers such as LVDTs and magnetostrictive devices.

An impact test determines the energy absorbed in fracturing a test piece at high velocity and this usually involves a large range of displacement. Sometimes LVDT's are used, but more usually MTS Temposonics transducers are recommended because of their much larger measurement range. MTS Temposonics are the original developers of the magnetostrictive technology and recognised world leaders for quality and service for this very rugged type of sensor. Based on the magnetostrictive principle displacement sensors are extremely accurate, highly reliable, offer absolute position measurement, can easily be installed and enjoy long trouble-free performance.

Window frame deflection!

LVDTs and load cells used to check window frame deflections 

A combination of Linear Variable Displacement Transducers (LVDTs) and load cells can be employed to measure deflection in various components of window frames.

RDP Electronics Ltd offers a comprehensive range of both LVDTs and load cells that are used to obtain force versus displacement data for various parts of the frame structure. Analysis of this data provides information enabling the window manufacturer to be sure that both during the installation of the frame, as well as when it is in application, does not cause the aperture to change shape significantly. This is important to avoid exerting pressure on the glazing, which could result in the glass shattering.

Car door testing!

In the automotive industry, doors and bonnets of cars and trucks are routinely tested to confirm they will continue to perform for the designed life of the vehicle, or to determine when failure might occur. RDP can supply LVDTs and load cells for the purpose that offer the accuracy and longevity required making them ideally suited to such applications.

A pneumatic or hydraulic actuator is typically used to open and close the door for a pre-determined time or series of test cycles, using LVDTs to accurately measure displacement and load cells to measure the forces applied. Data can then be captured for further analysis. Because of the LVDTs inductive principle of operation with no electrical connection across the sensing element, they are inherently suitable for delivering clean data when working in long term testing regimes.

Level using LVDTs

Accurate means of measuring liquid level using LVDTs
          
Although there are various options for measuring liquid level in a tank, RDP Electronics are able to provide an LVDT based solution that can often be used where other methods are inappropriate.

Typically the LVDT is fitted with a weighted float and installed with the transducer directed vertically downward towards the liquid surface. This approach is often suitable where the liquid inside may form a foam on top, precluding the use of optical devices. LVDTs can also be used in some Intrinsically Safe (IS) applications where the liquid may be flammable or surrounded by explosive gas, which could exclude many other types of devices. Where there is a risk of liquid rising too high in the tank, then the use of submersible version LVDTs will ensure the device is adequately protected, while the fully stainless steel body of the transducer reduces concern for deterioration in corrosive or saline fluids. The RDP range also includes seawater submersible versions of the SS Series.

VDTs for hydraulic proportional control

Thanks to their ability to be immersed or flooded by non-corrosive and non-degrading oils often used in hydraulic systems, LVDTs from RDP Electronics are ideal for providing feedback for control valve positions.

Proportional valve control can be used to manage direction and amount of fluid flow, or pressure within a system, are particularly useful in situations where system speed must be tightly controlled and where ramping up and down is needed to avoid sudden starts or stops. They can also provide precise control in applications where hydraulic pressure must be built up steadily. Because RDP’s LVDTs have a have a high-speed response and operational suitability over a wide range of temperatures, they can usually be incorporated in many proportional control valve applications.

Avoiding pipe fractures

Monitoring to avoid pipe fractures from oscillations
          
Oscillations in pipework that could lead to fatigue fractures and subsequent serious plant problems can be monitored by LVDTs to check for early indications of excessive movement.

On large sites, such as in the processing and petrochemical industries, or in power stations, the motion of structures can set up oscillations in the pipework around various parts of the plant. Pipework oscillations are undesirable because they can cause fatiguing in the pipework and additional stressing on other components in the plant that can lead to fracturing. These pipes may be carrying hot and dangerous liquids or chemicals. Very often oscillations are as a result of the feed through rate, or the process rate in the plant where a certain loading or flow rate through the plant may create a situation which causes a particular section of pipework to begin to oscillate.

RDP Electronics' LVDTs are designed and manufactured, for accuracy and reliability and have been used extensively to monitor movement in pipework. LVDTs are also available in versions well suited to locations where the pipes are hot and even for use in situations where pipes are carrying corrosive or radioactive substances.

Measuring Displacement

An informative guide to aid LVDT selection

Monitran has produced an easy-to-use and informative selection guide for its Linear Variable Differential Transformers (LVDTs).

The guide details Monitran’s Miniature, Industrial and Economy LVDTs; which between them have stroke lengths ranging from ±0.25 to ±550mm.

Selection criteria include mechanical/physical characteristics such as construction material, assembly type, cable exit type, operating temperature range and sealing. Electrical characteristics include degree of linearity and output type.

Andy Anthony, Monitran’s Operations Director, comments: “The LVDT is a well-proven, reliable and rugged transducer type for measuring displacement. At Monitran we make all LVDTs to order, so that they can match our customers’ exact requirements.”

Monitran’s Miniature LVDTs are ideal for applications where space is at a premium, the Industrial LVDTs are the most rugged and are ideal for use in harsh environments, and the Economy LVDTs are an extremely cost-effective solution for all less demanding applications.

Blast & recoil testing

RDP Electronics Ltd can recommend and supply Linear Variable Displacement Transducers (LVDTs) suitable for measuring deflections of structures during blast testing.

Typically used for determining deflection of walls, wall panels and metal structures, RDP long stroke transducers, with small additional protection and with support for the armature against side forces, have proved suitably robust to withstand repeated testing of blast structures. LVDTs are usually mounted within an outer tube which covers the exterior of the body. Similarly installed, LVDTs have also proved their worth in recoil testing, particularly testing of large projectile launchers in various applications.

Flanged LVDTs provide integrity for pressure vessel measurements

RDP Electronics  are often called on to provide flanged or seal threaded versions of their Linear Variable Displacement Transformers (LVDTs) for displacement measurement in pressure vessels.

Because it is not always possible to simply place an LVDT within a pressure vessel a flanged version with the armature pointing into the vessel that maintains the pressure integrity can provide the solution. This may be by means of a flange or alternatively a threaded seal integral with the body of the LVDT. Many types of LVDT from RDP’s comprehensive range have been supplied to suit different customer requirements including the LIN series where pressure additionally associated with high temperatures is involved.

Crack movement

Monitoring movement of cracks in structures with LVDTs

Measuring the changes in the width of cracks that occur in civil structures and buildings can be accurately determined by the use of Linear Variable Displacement Transducers (LVDTs). This important diagnostic technique can provide data to help understand the cause and then action appropriate remedial work where needed.

Transducer solutions specialists RDP Electronics offer a comprehensive range of LVDTs including waterproof options for use in external applications and harsh environments. Using analogue versions with a 4-20mA facility permits the use of long cable runs which can prove a useful capability where location of monitoring equipment is remote from the crack location.

Transducers ideally suited to tests involving shock and vibration

Linear variable displacement transducers (LVDTs) from RDP Electronics are inherently robust and durable enough to meet the rigours of testing in situations generating vibration or shock.

Such test situations are numerous, but typical applications include vehicle testing, recoil testing, switchgear testing, and use on rolling mills and steel production machines, which often involve high levels of shock and vibration. Thanks to the rugged LVDT technology they have a high cycle life, excellent accuracy and repeatability with the added advantage of being an absolute device with infinite resolution. Because the sliding core of an LVDT does not touch the inside of the tube in which it is housed, it can move without friction, making the LVDT a highly reliable device, while the absence of any sliding or rotating contacts allows the device to be totally sealed. Typically the housing is of stainless steel providing high levels of protection against the operational environment. RDP offers comprehensive ranges of LVDTs for many types of accurate displacement measurement.

Displacement measurement in pressure test vessels

Accurately measuring displacement in pressure test vessels demands robust, miniature transducers that are designed to withstand tough conditions. RDP Electronics offers several ranges of linear variable displacement transducers (LVDTs) that can withstand not only the pressures involved but where required submersion in water and oils – even combinations of pressure with high temperatures in some extreme cases.

Testing typically involves soil, rock and core samples and according to the precise requirement, LVDTs from RDP’s D5, PY and LIN ranges can provide the appropriate solution. Designed for use while submerged in fresh water, most corrosive liquids and gases, RDP’s D5 transducer series offers micron accuracy, can be sealed to withstand pressures up to 34 bar and is well suited to soil testing. Options include unguided and spring operated versions and a choice of end (axial) or side (radial) connections.

For component testing, the compact PY range is ideal for use where access or mounting space is limited, as it uses the variable reluctance principle to measure the distance of a metallic target over ranges of 1.5mm to 6mm from the transducer's body without any direct contact. Finally, the LIN transducer is suitable for submersion and capable of working at temperatures up to 450°C or pressures of 200 bar. The standard range of LIN transducers are available for measurement ranges from ±5 mm up to ±25 mm and as well as withstanding extreme high and low temperatures are also suitable for environments subject to exposure to radiation.

Miniature LDVT’s

For embedded automotive and laboratory test bench applications

Meggitt Sensing Systems has announced the North American market debut of the Sensorex model SX9W3, a rugged, high-accuracy miniature linear variable displacement transducer (LDVT), designed for high-precision displacement measurements within a variety of embedded automotive and general laboratory test bench applications.

With an overall length of just 26 mm (with body and core at null position) and a 9 mm diameter, the instrument offers a maximum linearity error of less than ±0.25% of full scale, with option to further reduce to ±0.15% of full scale. The transducers are designed to reliably operate over an operating temperature range of -40°C to +125°C (-40°F to +257°F) and are environmentally sealed to IP65. Meggitt’s Sensorex LVDT’s have no wearable parts for friction-free operation, while offering infinite resolution, long service life and high measurement repeatability. Units are highly resistant to shock and vibration, impervious to external magnetic fields and are designed to be compatible for use with all industry standard LVDT signal conditioners. The low mass of the Sensorex model SX9W3 core LVDT assembly makes the transducer ideal for use in applications where high-reliability displacement measurements are required, though where mass, weight and space constraints may be of concern.

Recommended accessories for the Sensorex model SX9W3 include the model SX3120 DIN rail signal conditioner for industrial applications, as well use of an MCHP conditioner for integration with electronic boards. In addition, a spare core assembly, mounting flange, and custom calibration and core assemblies are available upon request. All Sensorex model SX9W3 miniature LVDT’s are accompanied by a two-year comprehensive product warranty and are available thru both Meggitt’s San Juan Capistrano, California, USA and Archamps, France-based facilities